President Barack Obama's tumbling poll numbers have dipped below those of his predecessor George W. Bush at the same point in his White House tenure, according to a national poll released on Tuesday.

Obama's approval rating is 55 per cent six months into his presidency, a USA Today/Gallup poll found. But 56 per cent of those polled approved of the job done by George W. Bush after six months, the daily reported.

Obama's handling of the economy appears to be key in his fading popularity, as Americans become more pessimistic about how long it will take the economic downturn to end.

"His ratings have certainly come back down to Earth in a very short time period," Republican pollster Whit Ayres told the daily. By 49 per cent to 47 per cent, respondents said they disapprove of Obama's handling of the economy, while they disapprove of his health care policy by 50 per cent to 44 per cent.